No abstract

Chemical turbulence was observed experimentally in the 1,4-cyclohexanedione Belousov-Zhabotinsky (CHD-BZ) reaction in a double layer consisting of a catalyst-loaded gel and uncatalyzed liquid on a Petri dish. The chemical patterns...

Background: Vaccinations are the best hope to control the COVID-19 pandemic and save lives. Due to the high demand and failure to share vaccines equitably, there were not enough vaccine supplies to cover the majority of people in low- and middle-income countries during the early stage of vaccination. To cope with this problem, Thailand, an upper-middle-income country, decided to employ a heterologous vaccination strategy as the primary COVID-19 vaccination regimen in the country. The CoronaVac (CV) vaccine was administered as the first dose, followed by the ChAdOx1 nCoV-19 (AZ) vaccine as the second dose. However, there is no study to assess the effectiveness of the heterologous vaccination employed in Thailand compared to the standard homologous vaccination. Methods: We delineated the course and timeline of COVID-19 vaccination in Thailand. An age-structured compartmental model for COVID-19 transmission and vaccination was constructed and employed to assess the effectiveness of the heterologous vaccination strategy. The impact of the vaccine prioritization strategies on COVID-19 mortality and infections was also investigated. Results: We found that the CV+AZ heterologous vaccination strategy outperforms the CV and AZ homologous vaccinations in reducing cumulative cases and deaths when combined with other non-pharmaceutical interventions. Furthermore, the results suggested that prioritizing vaccines for the elderly could be optimal in reducing COVID-19 mortality for a wide range of vaccination rates and transmission dynamics. Conclusions: Our modeling results suggested that to minimize inequity in COVID-19 vaccine access in low- and middle-income countries, those countries may use early accessible but maybe lower-efficacy vaccines as the first dose of heterologous vaccination in combination with higher-efficacy vaccines as the second dose.